This invention relates to latency control in communication devices. More specifically it relates to a method for mapping packet service categories to latency paths in asymmetric digital subscriber line transmission systems.
Many applications used from digital computers are asymmetric. For example, video on demand, Internet access, intranet access, remote local area network access, multimedia access, are specialized services that typically require high data rates downstream, but have relatively low data rates demands upstream.
An Asymmetric Digital Subscriber Line (xe2x80x9cADSLxe2x80x9d), is a communications technology that transmits an asymmetric data stream over a conventional twisted pair of telephone wires. An Asymmetric Digital Subscriber Line transmits a larger data rate downstream to a subscriber from a telephony switching office than from a subscriber back to the telephony switching office. Asymmetric Digital Subscriber Lines typically transmit about 1.5 Mega bits-per-second (xe2x80x9cMbpsxe2x80x9d) to about 9 Mbps downstream to a subscriber, and about 16 kilo-bps (xe2x80x9ckbpsxe2x80x9d) to 640 kbps upstream back to a telephony switching office. The asymmetric data rates depend on a number of factors, including length of the twisted pair of copper wires, copper wire gauge, and cross-coupled interference.
An ADSL system typically comprises two asymmetric devices connected by a conventional twisted pair of copper wires. An ADSL Transmission Unit-Central (xe2x80x9cATU-Cxe2x80x9d) is a device at one end of an ADSL connection at a telephony or other switching office. An ADSL Transmission Unit-Remote (xe2x80x9cATU-Rxe2x80x9d) is a device at another end of an ADSL connection at a subscriber or customer site.
The ATU-R may be integrated into a service module. A service module typically converts received digital signals into signals suitable for particular subscriber or customer premise equipment. The ATU-C may be integrated within an access node. An access node typically includes digital loop carrier systems such as a Digital Subscriber Line Access Multiplexer (xe2x80x9cDSLAMxe2x80x9d) concentrating individual connections to T1 lines, E1 lines cellular antenna sites, Private Branch Exchanges (xe2x80x9cPBXsxe2x80x9d), Optical Network Units (xe2x80x9cONUsxe2x80x9d) or other carrier systems.
ADSL systems typically use Discrete Multi-Tone Modulation (xe2x80x9cDMTxe2x80x9d) for data transmission. Low speed services, such as Plain Old Telephone Service (xe2x80x9cPOTSxe2x80x9d), are carried in a baseline modulation frequency or low frequency, while higher speed multimedia services are modulated at higher frequencies.
Some applications require transport of packet data. An Asynchronous Transfer Mode (xe2x80x9cATMxe2x80x9d) system can use high-speed services on ADSL systems as a physical layer to transport data packets. As is known in the art, ATM is a high-speed packet transmission mode. ATM segments and multiplexes data traffic into small, fixed-length units called xe2x80x9ccells.xe2x80x9d A cell is 53-octects, with 5-octects for the cell header, and 48-octects for the cell data. ATM provides four services category classes that may use constant bit-rates, variable bit-rates, available bit-rates and unspecified bit-rate services.
Another high-speed packet transmission mode includes Frame Relay. As is known in the art, Frame Relay is packet-switching protocol for use on wide area networks (xe2x80x9cWANsxe2x80x9d). Frame relay transmits variable-length packets at up to 2 Mbps over predetermined, set paths known as PVCs (permanent virtual circuits).
Another mode of packet transmission includes the Internet Protocol (xe2x80x9cIPxe2x80x9d). As is known in the art, IP is a routing protocol designed to route traffic within a network or between networks. Voice over Internet Protocol (xe2x80x9cVoIPxe2x80x9d) is a protocol that can be used to send voice information in IP packets.
An ADSL system typically includes one or more xe2x80x9csplitters.xe2x80x9d Splitters are filters that separate high frequency and low frequency ADSL signals. A splitter may be integrated into ATU-C or ATU-R, physically separated from the ATU-C or ATU-R, or divided between high pass and low pass functionality, with the low pass functionality physically separated from the ATU-C or ATU-R.
An ADSL system can also be used without splitters. The Splitterless ADSL standard is called xe2x80x9cG.lite.xe2x80x9d G.lite is a new standard that uses DMT baseline modulation delivering a maximum downstream bandwidth of up to 1.4 Mbps, but is less sensitive to noise and other transmission problems.
Two modes of latency have been specified for ADSL systems. The purpose of latency is to provide a data path through an ADSL system that can be used to provide a service category. For example, a data path can be provided between an ADSL transmission unit and a virtual circuit connection for a transport protocol such ATM, Frame Relay or others. A data path can also be provided between an ADSL transmission unit and a packet connection for a customer premise distribution protocol such as the Internet Protocol. The latency path is used for carrying user traffic that has different service requirements in terms of delay and reliability. Generally, two latency paths are defined: a xe2x80x9cFastxe2x80x9d path and an xe2x80x9cInterleavedxe2x80x9d path. The Fast latency path corresponds to a lower reliability, shorter delay path. The Interleaved latency path corresponds to higher reliability, longer delay path.
There are several problems associated with using latency paths between ADSLs and the Internet Protocol or other protocols used on premise distribution networks. One problem is that it is possible to use three or more latency classes on a latency path including: (1) single latency, that is not necessarily the same for each direction of transmission; (2) dual latency downstream with single latency upstream; and (3) dual latency both upstream and downstream. Multiple latency classes on a single latency path complicates any latency mapping.
Another problem is since the functionality of a latency path is typically located in a transmission convergence sub-layer, a mapping mechanism is necessary to map a service request to a corresponding latency path. However, most mapping mechanisms known in art are dependent on the architecture of the transmission sub-layer and vary with the type of transmission hardware being used. In addition, most mapping mechanisms known in the art do not provide a mechanism to map service category request, such as quality-of-service requests to a latency path at an ADSL transmission convergence sub-layer.
Since a latency path is typically located in a transmission convergence sub-layer, an additional mapping mechanism at a service specific convergence sub-layer may also be needed if a network is using a customer premise distribution network protocol such as the Internet Protocol, that allows Type-of-Service categories to be used.
Thus, it is desirable to have a generic mapping procedure that will map a service category request from a customer premise distribution network to an ADSL latency path. The generic mapping procedure should also be independent of the underlying architecture of the system it is used on and provide the ability to map service category requests including Type-of-Service requests, from premise distribution network protocols to a latency path on an ADSL system.
In accordance with preferred embodiments of the present invention, some of the problems associated with mapping packet service category requests to ADSL latency paths are overcome. A method and system for mapping packet service categories to ADSL latency paths is presented.
One aspect of the invention includes a method for mapping outgoing data packet service categories to latency paths in an asymmetric data transmission system. The method includes creating a desired ADSL latency mapping for desired service category requests for outgoing data packets in a customer premise distribution network protocol and packing the outgoing data packets into outgoing data cells in a transport network protocol using the latency mapping.
Another aspect of the invention includes a method for transparently transferring information from incoming data cells from a transport network in a transport protocol with a desired service category and a pre-determined latency mapping, into incoming data packets for a customer premise distribution network protocol.
Another aspect of the invention includes a latency mapping system for an asymmetric data transmission system. The system includes a latency mapping policy, a service specific convergence sub-layer and a transmission convergence sub-layer. However, the latency mapping system may have more, fewer or equivalent components and is not limited to the three described components. The latency mapping policy is used for mapping a desired service category for a customer premise distribution protocol to an asymmetric digital subscriber line latency path. The service specific convergence sub-layer examines service category requests from outgoing data packets, maps service category requests to an ADSL latency path, packs outgoing data packets for a customer premise distribution protocol into multiple data cells for a transport protocol and re-assembles information multiple incoming data cells from a transport network into multiple incoming data packets for a customer premise distribution protocol. The transmission convergence sub-layer accepts multiple outgoing data cells in a transport protocol created from multiple outgoing data packets for a customer premise distribution protocol with a determined asymmetric digital subscriber line latency mapping for a desired service category request, and accepts multiple incoming data cells in a transport protocol with a pre-determined asymmetric digital subscriber line latency mapping for a desired service category request.
The present invention may help overcome some of the problems associated with packet service category latency mapping to ADSL links. A mapping to latency paths on ADSL system may allow differential services to be provided for user data from a customer premise distribution network based on a desired packet service category. The latency mapping mechanism at an ADSL link may help provide end-to-end virtual connections over real-time ADSL links.
The foregoing and other features and advantages of preferred embodiments of the present invention will be more readily apparent from the following detailed description. The detailed description proceeds with references to the accompanying drawings.